A 0.7-V 28-nW CMOS Subthreshold Voltage and Current Reference in One Simple Circuit

Abstract

This paper presents a low-power and high-precision voltage and current reference (VCR) in one simple circuit. The voltage reference is derived from the threshold voltage difference between an I/O (i.e., 3.3-V NMOS) and standard (i.e., 1.8-V NMOS) transistors with temperature-independent bias current, and the current reference is the voltage reference divided by a temperature-insensitive resistor. The resistor is made up by series connection of a proportional-to-absolute-temperature (PTAT) NWELL resistor and a complementary-to-absolute-temperature (CTAT) high-resistance poly resistor in series. Implemented in a standard 0.18-μm CMOS process, the proposed VCR circuit takes an active area of only 0.055 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured voltage and current references (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> ) at room temperature are 368 mV and 9.77 nA, respectively. The measured average temperature coefficient (TC) of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> are 43.1 ppm/°C and 149.8 ppm/°C over a temperature range of -40~125°C with one-time trimming and the variation coefficients are 0.35% and 1.6%, respectively. The measured voltage and current line sensitivities are 0.027%/V and 0.6%/V, respectively. The minimum supply voltage is 0.7 V with a total power consumption of 28 nW. The measured power supply ripple rejection (PSRR) of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> is -65 dB @DC and -39.4 dB at frequencies higher than 1 Hz.